Process for deodorizing and sterilizing air



Jly 6, 1954 R, L. KUEHNER PROCESS FOR DEoDoRIzING AND STERILIZING AIR Filed Nov. 2e, 1949 nvenfor Cttornegs AIR. FLOWS Fic-3,4-

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Richard L.Kuehner AIR FLOWS AIR. FLOWS APatented July 6, 1954 PROCESS FOR DEODORIZING AND STERILIZING AIR Richard L. Kuehner, Springgarden Township, York County, Pa., assignor to York Corporation, York, Pa., a corporation of Delaware Application November 28, 1949, Serial No. 129,725

2 Claims.

This invention relates to improvements in air conditioning systems and is more particularly 'directed to a method and means for purifying and improving the quality of air in occupied enclosures so as to render the air free of odors, sterile and comfortable at all times. It is a speciic object of the invention to reduce odors, bacteria (both harmful and non-harmful) and molds in circulated air.

The invention makes it possible to furnish in an inexpensive manner an abundant supply of sterile air which, in addition to being cooled and dehumidifled'approaches in characteristics normal fresh outside air.

In air conditioning systems employing recirculation of air, there takes place a rapid build-up of bacteria and odors and the concentration of these components eventually exceeds the human toleration level. It has been attempted, in the past, to remedy this situation by diluting the inside air with a continuous supply of fresh outside air; it will be apparent, however, that this solution entails the provision of excessively large equipment for dehumidifying and tempering the continuously added fresh air, thereby increasing not only the initial cost of the installation, but also the operating and maintenance costs.

In contrast with prior attempts, this invention permits reduction of odors, bacteria and mold concentrations in conditioned air to satisfactory levels Without the addition of excessively large quantities of fresh outside air for dilution purposes, or the incorporation of expensive equipment. My invention resides in treating the air to be purified with a chemical mixture which has the property of removing odors, bacteria and molds therefrom. In particular, I have discovered that excellent results are obtained by treating odor and bacteria-laden air with an aqueous alkaline solution `of potassium permanganate. That is, I have found that an alkaline solution of potassium permanganate is more effective for removing odors, bacterias and molds and improving the condition of the treated air than is potassium permanganate alone. Fundamentally, the action of my treating solution is one of oxidation, which is performed by the permanganate, but I have discovered that the presence of the alkalizing agent is essential for the practical and efficient use of the permanganate for the following reasons:

1. The disinfectant qualities of potassium permanganate are increased in an alkaline solution;

2f The deodorant qualities of potassium permanganate are increased in an alkaline solution;

3. Potassium permanganate is less corrosive in an alkaline solution and, therefore, less harmful to the equipment, and

4. Potassium permanganate has no tendency to spontaneous, useless breakdown in an alkaline solution.

The use of an alkaline treating solution is additionally highly advantageous from the standpoint of preventing contact of equipment with an acid menstruum which corrodes the equipment Wherever there is a water-metal contact. Further, an acid menstruum renders KMnOl corrof sive and also causes the spontaneous breakdown of the KMnO4. It is apparent, therefore, that the use of KMnO4 in an alkaline solution is not only directly beneficial in that the disinfectant and deodorant qualities of the permanganate are enhanced, but is further desirable from the standpoint of the preservation of equipment and the stability of the treating solution.

In actual practice, using high concentrations of chemicals in the treating solution, comparative tests with (a) a neutral permanganate, and (o) alkaline permanganates-e. g. a sodium hydroxide-potassium permanganate mixture and sodium bicarbonate-potassium permanganate miX- ture-have shown that air treated with the alkaline permanganate has at least 45% less odor than air treated with the neutral permanganate, all other conditions being the same. In fact, in the case of the bicarbonate, the air contained about 58% less odor. 4used in low concentrations, the superiority of the alkaline solutions persists. Moreover, the use of the alkaline solution of the present invention gives uniform, high and rapid bacteria kill and mold destruction, as contrasted with the sporadic effect of thevneutral permanganate solution.

As evidence of the improved results which are obtained by the use of my alkaline solution of potassium permanganate for deodorizing, I am setting forth below the data obtained with comparative tests. In these tests, cigarettes were burned directly into three tubes of the different test solutions, respectively containing (l) neuh tral potassium permanganate, (2) potassium permanganate alkalized with NaOI-l, and (3) po.- tassium permanganate alkalized With NaHCOa. The residual odor left in the air after passing through the tests solutions under identical conditions, was measured by determining the amount of a standard KMnO4 test solution reduced by the residual odor. My experiments over a considerable number of years have indicated that this procedure constitutes an accurate and precise When the chemicals are' method of measuring odors, the concentration oi odor being directly reflected by the amount of KMnOi reduced. The numerical data yielded by the tests are set out below:

Residual odor left in air after passing through high concentration 'neutral and alkaline Kil/[n0g under identical conditions Solution reduced by residual odor in air stream Treating Solution after deodorlzation Neutral KMnOi KMnOi and NaOH..- KMnOi and NaHCOa 6.28 inl. N/l0 KMnOL 3.48 ml. N/l0 KMnOi. 2.67 ml. N/lO KMnOi.

Comparison of the figures readily shows that the residual odor left in the air after passing through a solution alikalized with NaO-I-I is much less, by

628 X 100 or 45%, than that left after passage through a neutral KMnO4 solution, since the residual odor reduced 3.48 ml. ci the odor measuring test solution, as against 6.28 when the air was preliminarily treated with neutral permanganate solution. Still better results were obtained when air was preliminarily treated with a permanganate solution alkalized with NaI-1G03, since the residual odor was only capable of reducing 2.67 ml. of the odor measuring test solution and, hence the residual odor left in the air in this instance is of air conditioning or treating system. The more intimate the contact of the air with the treating solution, the more effective is the treatment according to my invention. In practice, excellent results are obtained by passing the air stream to be treated through a curtain of nely divided particles of the treating solution. The chemical is effective when distributed in bumidifying sprays, whether in the washer type or the dry type. In the case of dry systems, I have found that particularly good results are obtained by pouring the solution of the chemical on top of the cooling coils with the air owing upwardly through the solution between the i'inned coils. However, it is to be understood that the practice. of my invention is not limited to the spraying of the solution into the air stream or to the passing of the solution over finned coils, between which the air to be treated passes. Any apparatus which gives an intimate contact between the air and the treating solution is satisfactory for the purpose of my invention. Thus, the solution can be poured over metal or glass Wool or bers through which is passed the air to be treated.

To render the aqueous potassium permanganate solution alkaline, there can be used any suitable alkalizing compound having a cation which does not react with the permanganate radical, since such reaction would precipitate the anion MnOi from the solution and thereby render it ineffective. I have successfully used Sodium bicarbonate and alternatively, sodium hydroxide to form the alkaline solutionmixture. While sodium hydroxide is a good alkalizing agent and increases the activity of the potassium permanganate as an air deodorant and disinfectant, the use of the bicarbonate is preferable. Among other advantages, the bicarbonate exerts a buffering action to maintain the alkalinity of the solution mixture, notwithstanding the presence of substantial amount of CO2 in the air being treated. This is so, because oi the excessive presence of the bicarbonate ion which prevents the dissociation of the dissolved carbonio acid and, accordingly, inhibits solution oi undue amounts of CO2 from the air into the treating liquid. The treating solution is therefore maintained continuouslyA basic. In other words, the bicarbonate radical does not react with the carbonio acid but only suppresses its concentration by reducing the solubility of CO2 in the water. I have determined that only 0.05 gram of sodium bicarbonate per liter oi liquid will retain that liquid decidedly alkaline, no matter how much air is passed through it.

This buiering action of the sodium bicarbonate constitutes an important ieature of my invention because its mere presence in even minute quantities prevents the water menstruum from becoming acidic. The use of sodium bicarbonate in the treating solution does not invo ve a chemical reaction resulting in inert residues or a pile of end products which must be cleaned out periodically. The addition oi sodium bicarbonate maintains a given alkalinity in the solution over an indefinite period of time. It is apparent that the advantageous buffering action or" sodium bicarbonate may be utilized in all instan-ees where air or other gases are treated with an aqueous medium and it is desired to inhibit the acidification of the aqueous medium by the absorption of CO2 from the gas being treated.

As explained above, the eiiectiveness of the potassium permanganate solution is substantially improved by utilizing a solution mixturewhich is at all times maintained on the alkaline side. In preparing suitable treating solutions, the ratio by weight or sodium bicarbonate to potassium permanganate is about l to 2.5 and the weight oi permanganate per liter of water ranges from 0.13 gm. to .25 gin. In the case of sodium hydroxidepotassium permanganate solution, the ratio of the Weight of sodium hydroxide to the weight of potassium permanganate used is l to 2.5, and the amount by Weight of potassium permanganate per liter of water ranges from 0.13 gm. to 0.25 gin. While I have mentioned sodium hydroiide sodium bicarbonate, it is to be understood that any of the other alkali metal and alkali earth metal hydroxides and bicarbonates may be used, as long as they, or any other alkalizing agent, do not contain a cation which precipitates the permanganate radical as above mentioned. The important feature of the invention is that the solution mixture is always on the alkaline side.

In order to econornize in the use of chemicals, it is my aim to use the most dilute treating solution possible, especially in air washer systems where there is a continuous or intermittent overflow or the washer solution clown a drain due to the condensation of moisture from the air. The lower limit for the concentration of potassium permanganate per liter of Water was determined by the ability of the solution to kill certain coinmon airborne pathogenic bacteria in a specified period of time. In a normal washer the water gesehn makes one recirculation in 40 seconds. Accordingly, it is theoretically possible, although improbable, that a pathogenic organism can enter the washer system from the air and be discharged back into the air within i0 seconds. Therefore, I have determined by experiments that lower limit of concentration of alkalized potassium permanganate which destroys these pathogens within 40 seconds. This lower limit -is 0.13 gram of potassium permanganate per liter of water, as specified above. The reaction of the oxidant with the odor will take place in any concentration but will, of course, follow the law of mass action in that the speed will vary with the concentration. Therefore, the lower limit was established on the basis of the germicidal properties of the resultant `solution and, for proper effectiveness, the concentration must not drop below this specied minimum. But I can go to any concentration above this minimum, which fits the particular application. The range of 0.13 to 0.25 gram of permanganate per liter of water is a practical range, based on my experiments. These established that one charging of the washing water to the maximum concentration-le. 0.25 gram of potassium permanganate per liter of water-would last for one week in a practical washer system without dropping below the minimum concentration of 0.13 gram. Concentrations higher than 0.25 may, of course, be

used but, where there is an overflow of the solution down a drain, it is economically unsound to use higher concentrations because of the useless waste of chemicals. It should be pointed out that the value given above for the minimum concentration of potassium per-manganate in the treating solution is based upon an assumed time of contact between the air and the treating solution.

However, where a longer time of contact than I trated several systems in which the invention finds useful application but, as heretofore indicated, the invention is not limited to any specific system. In the drawings,

Figure 1 is a diagrammatic view of a typical washer using my invention;

Figure 2 is a diagrammatic View of a typical embodiment of my invention in a dry coil unit;

Figure 3 is a diagrammatic view of my invention applied in a typical air washer system which may or may not be associated with a refrigerating unit;

Figure 4 is a diagrammatic view of a simple form of unitary apparatus for carrying o-ut my invention, and

Figure 5 is a diagrammatic view of still another form of apparatus for carrying out my invention.

Referring toFigure 1, the unit has the usual spray devices I0 for spraying the treating liquid, and which are interposed in the path of the air stream which enters the compartment Il at one end I2 thereof and leaves at the other end I3. The liquid circulating means is indicated at I4,

\ the liquid accumulating in the bottom of the compartment to the level indicated at I5.

The chemicals may be added to the treating water in the compartment, or the water may be preliminarily prepared by adding the chemicals thereto and introducing the same to the circulating system. The chemicals mayv be introduced to the treating water-individually or as mixtures in the form of dry powders, concentrated aqueous solutions or as pills or tablets,

whichever is considered most convenient. The numeral IB indicates a suitable receptacle for replenishing the chemicals in the solution to maintain the desired concentration thereof, and

' this receptacle may be manually operated to dispense chemicals into the circulating solution mixture, or suitable means may be provided for automatically carrying out the dispensing, either continuously or intermittently in the case cf the powder or concentrated solution, and intermittently in the case of tablets or pills. Such automatic dispensing means are well known in the art and may be controlled by any one of the factors characteristic of the circulating solution-e. g. departure from its normal concentration or color intensity.

In the practical operation of my invention, the rate of addition of the treating chemicals can be readily varied in order to meet the odor load. As will be appreciated, this rate of addition of the chemicals must also take into consideration the type of air treating system used that is, whether it is of the overflow or non-overflow type. Thus, in the case of air washer systems where there is acontinuous or intermittent overow of thekwasher solution clown a drain due to the condensation of moisture from the air, both the alkalizer e. g, the bicarbonate and the potassium permanganate may be made up continuously. In other types of installations replenishment of chemicals need only take place at rare intervals. In one type of washer system used experimentally by me, the addition of chemicals was only made once a week.

In Figure 2-in which the same reference numerals are used for the same parts except that they also have a differentiating letter-the unit diiers from that of Figure 1 only by the presence of a bank of cooling coils Il interposed in the compartment IIa and through which the air stream passes. In Figure 3 the unit is substantially the same as shown in Figure 1, except that a fan I8 is used at the inlet end I2b of the compartment 1lb, and eliminator rbaiiies I9 are provided at the exit end |313. A refrigerating unit 20 may be employed with this unit, in which event, the solution will be circulated therethrough. However, the use of this refrigerating unit is not necessary and it can be omitted. The apparatus shown in Figure 3 may be used either .as a deodorizer and sterilizer, or for cooling the air as well.

Figure 4 illustrates a unitary apparatus-generally represented by the numeral llc-for carrying out my invention and consisting of no more than the chemical reservoir Hic, pump I4c, sprays Ic and eliminator baiiles Iilc combined as a unit adapted for incorporation in any duct through which air is passing. .As will be observed. no blower is used in this instance and thecombination is of such a nature that it can be easily inserted in the air duct of any air conditioning or Ventilating system, whether new or old, or can be attached to the side, or within, any air conditioning unit.

, in this manner intimate contact of the air with the tlnely divided liquid particles is obtained. My invention is however not restricted in its application to arrangements in which the chemical solution used for treating the air is sprayed into the air or sprayed onto coils, as in the embodiments illustrated in Figures I to 4. Any other means for contacting the liquid with the air or subjecting the latter to treatment with the improved solution mixture may be employed. I can use an arrangement, as illustrated diagrammatically in Figure in which the chemical solution is poured on the top of any brous or granular material 2| through which it trickles down and this material, wetted with treating solution, presents a large contacting surface for the air stream passing therethrough. Any material can be used which is non-reactive with the disinfectantdeodorant chemical treating solution. I have successfully used glass Wool, brass wool and copper mesh fillers.

It will be seen, therefore, that my invention consists in treating the air to be puried with an aqueous solution of a mixture of inexpensive, nontoxic, non-corrosive readily available compounds. I have discovered that when these chemicals are present in the air treating solution in concentra-- tions above a certain minimum, as above described, they effectively remove odors of various types, including body odors and cooking odors, bacteria and molds from an air stream rendering the latter odorless and sterile, so that the treated air actually contains less odor and bacteria than normal, fresh outside air. The use of the invention put no toxic or irritant vapors into the air and leaves no large quantities of inert residue to be cleaned out of the system, and actually keeps the system free of dirt, grease and other organic accumulations. These results can be obtained in practical air conditioning systems Without change in the operating procedure. Additionally, in the case of Washer type air conditioning systems, the presence of my air-sanitizing compound in the wash Water eliminates the necessity for the regular cleaning of the system to prevent contamination of the air by the accumulation of microbes and odors in the `dirty wash Water. This constitutes a considerable savings in expense and time since the average washer system must be vcleaned out once a Week. In contrast with this, a system containing my disinfectant-deodorant mixture may require cleaning but once a season or once a year.

As will be apparent from the foregoing description, my invention has universal adaptability and fits all types of air conditioning and Ventilating systems, humidica'tion and dehumidification systems or can be embodied in a separate unitari,7 system. My invention is adapted for use at all seasons of the year and the chemical v'treating solution can be used for deodorizing and sterilizing air in spaces even in the absence of means for dehumidifying and tempering the air.

What is claimed is:

1. In the process of deodorizing and sterilizing air circulated in occupied enclosures by bringing the air in intimate contact with an aqueous solu tion of potassium permanganate in which the permanganate is present in the amount `of at least 0.13 gramme per litre of Wat-er, the improvement of advantageously inhibiting the acidification of the aqueous solution by absorption of CO2 from the air which consists in: adding a buler compound to the aqueous solution, said compound being selected from the group consisting of alkali metal and alkali earth metal bicarbonates, and lbeing present in an amount effective to maintain the solution alkaline.

2,. lrocess according to claim 1, in which the buffering agent is NaHCOs and is present in the amount of at least 0.05 gramme per litre of Water.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,286,088 Pfanstiehl Nov. 26, 1918 1,942,485 Metzger Jan. 9, 1934 2,389,698 Stovvell Nov. 27, 1945 FOREIGN PATENTS Number Country Date 294,586 Great Britain July 27, 1928 OTHER REFERENCES Uses and Applications of Chemicals and Related Materials, by Gregory, Reinhold Pub Co. (1939), Vol. I, pgs. 483-4.

Chemicals Abstracts, vol. 22 (1927-1936 Decennial Index) page 1173. 

1. IN THE PROCESS OF DEODORIZING AND STERILIZING AIR CIRCULATED IN OCCUPIED ENCLOSURES BY BRINGING THE AIR IN INTIMATE CONTACT WITH AN AQUEOUS SOLUTION OF POTASSIUM PERMANGANATE IN WHICH THE PERMANGANATE IS PRESENT IN THE AMOUNT OF AT LEAST 0.13 GRAMME PER LITRE OF WATER, THE IMPROVEMENT OF ADVANTAGEOUSLY INHIBITING THE ACIDIFICATION OF THE AQUEOUS SOLUTION BY ABSORPTION OF CO2 FROM THE AIR WHICH CONSISTS IN: ADDING A BUFLER COMPOUND TO THE AQUEOUS SOLUTION, SAID COMPOUND BEING SELECTED FROM THE GROUP CONSISTING OF ALKALI METAL AND ALKALI EARTH METAL BICARBONATES, AND BEING PRESENT IN AN AMOUNT EFFECTIVE TO MAINTAIN THE SOLUTION ALKALINE. 